This was another one of those recipes that I knew from the moment I saw it that I had to make it. It was also the inspiration for buying a cake stand. I saw this months ago when Martha Stewart had the food blogger whose recipe it is on her show. The cake looks pretty unassuming on the outside so all of your guests will be surprised when you cut into it and pull out a bright rainbow. With the amount of eggs (19!) and butter (2 pounds!) and time (almost 3 hours) it really is only for special occasions.
Vegetable shortening (I used Pam)
3 cups all-purpose flour
4 teaspoons baking powder
1/2 teaspoon salt
2 sticks (1 cup) unsalted butter, room temperature
2 1/3 cups sugar
5 large egg whites, room temperature
2 teaspoons pure vanilla extract
1 1/2 cups milk, room temperature
Red, orange, yellow, green, blue, and purple gel food coloring ( I found it at Sur La Table)
In a large bowl, whisk together flour, baking powder and salt; set aside. In the bowl of an electric mixer fitted with the paddle attachment, cream together butter and sugar. Slowly add egg whites and mix until well combined. Add vanilla and mix until fully incorporated. Add flour mixture and milk in two alternating additions. Mix until well combined.
Preheat oven to 350F. Divide batter evenly between six medium bowls. Add enough of each color of food coloring to each bowl, whisking, until desired shade is reached. It takes a lot. Transfer each color to an individual cake pan. Spread batter in an even layer in the pan. Transfer to oven and bake until a toothpick inserted into the center of each cake comes out clean, about 15 minutes.
Remove cakes from oven and transfer to a wire rack; let cool for 10 minutes. Invert cakes onto a wire rack; re-invert and let cool completely.
Using a serrated knife, trim tops of cakes to make level. Mine were pretty flat so I didn’t trim them too much. Place four strips of parchment paper around perimeter of a serving plate or lazy Susan. Place the purple layer on the cake plate. Spread a scant 1 cup buttercream filling (see recipe below) over the first layer with a small offset spatula so it extends just beyond edges. Repeat process with blue, green, yellow, and orange layers.
Place the remaining red layer on top, bottom-side up. Gently sweep away any loose crumbs with a pastry brush. Using an offset spatula, cover the top and sides with a thin layer of frosting (also use any of the excess frosting visible between the layers). Refrigerate until set, about 30 minutes.
Using an offset spatula, cover cake again with remaining frosting.
The plain exterior…
and the amazing interior!
Lemony Meringue Buttercream
FOR THE FILLING AND CRUMB COAT
9 large egg whites
1 3/4 cups sugar
2 cups (4 sticks) unsalted butter, cut into small pieces, room temperature
2 teaspoons pure lemon extract
FOR THE FROSTING
5 large egg whites
1 cup sugar
1 cup (2 sticks) unsalted butter, cut into small pieces, room temperature
Make the filling and crumb coat: Cook egg whites and sugar in a small saucepan over medium heat, whisking constantly until sugar is completely dissolved. Transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until mixture is room temperature. With the mixer on medium-low, add butter, one piece at a time, mixing well after each addition.
Remove whisk attachment and switch to paddle attachment. Increase speed to high and beat until buttercream comes together, about 5 minutes; beat in lemon extract (I only put the lemon extract in the filling).
Make the frosting: In a clean saucepan and bowl of an electric mixer, repeat process in step 1.